MAVEN (Mars Atmospheric and Volatile EvolutioN) is the second mission selected for NASA's Mars Scout program, an initiative for smaller, low-cost, competed missions led by a principal investigator. Responsive to high-priority science goals listed in the National Academy of Science's 2003 decadal survey on planetary exploration, MAVEN is obtaining critical measurements of the Martian atmosphere to help understand dramatic climate change on the red planet over its history.

Long ago, Mars once had a denser atmosphere that supported liquid water on the surface. At that time, Mars might have had environmental conditions to support microbial life, as the long-term presence of water is necessary to life as we know it. However, as part of dramatic climate change, most of the Martian atmosphere was lost to space long ago. Features such as dry channels and minerals that typically form in water remain to provide a record of Mars' watery past, but the thin Martian atmosphere no longer allows water to be stable at the surface.

MAVEN is providing information on how and how fast atmospheric gases are being lost to space today, and inferring from those detailed studies what happened in the past. Studying how the Martian atmosphere was lost to space can reveal clues about the impact that change had on the Martian climate, geologic, and geochemical conditions over time, all of which are important in understanding whether Mars had an environment able to support life.

The first spacecraft ever to make direct measurements of the Martian atmosphere, MAVEN carries eight science instruments that are taking measurements of the upper Martian atmosphere. MAVEN can also dip to an altitude 80 miles above the planet to sample Mars' entire upper atmosphere. The spacecraft is able to provide communications relay support for landers and rovers on the Martian surface.